1. Field of the Invention
The present invention relates to a sensor for detecting defects in a component.
The component to be tested can be electrically conductive and ferromagnetic or non-ferromagnetic, and in this case the invention can detect defects such as surface or internal cracks.
The invention applies equally to detecting electrically conductive ferromagnetic or non-ferromagnetic particles in a material that is not electrically conductive.
2. Description of the Prior Art
Various techniques for non-destructive testing of metal components are known in the art: for example, Eddy current testing by measuring the impedance of sensing coils, or testing ferromagnetic materials by the dispersion flux method using magnetoresistive sensors. The document EP 0 736 173 B 1 describes, a sensor including an excitation coil whose axis is perpendicular to the surface of the product under test and which is fed with a varying electrical current to generate Eddy currents in the product.
The detector means include two Eddy current detector coils mounted in opposition and two magnetoresistors disposed parallel to each other and connected in a differential circuit. The Eddy current detector coils are coaxial with and inside the excitation coil and the magnetoresistors are parallel to the axial direction of the coils. The detector coils and the magnetoresistors are connected to processor means that include a multichannel processor circuit.
An object of the present invention is to propose a different sensor arrangement offering very high sensitivity.
The invention therefore provides a sensor for detecting defects in a component, the sensor including an electric coil fed with a varying electrical current to create a varying magnetic field penetrating at least partly into the component under test, and defect detector means including a giant magnetoresistor, the above components being accommodated in a protective housing having a detection face adapted to be disposed near and parallel to a surface of the component under test, the coil having its axis xcex94 perpendicular to the detection face, and the giant magnetoresistor being situated in the vicinity of the detection face and disposed so that its sensitivity axis xcex941 sensitive to variations in a magnetic field is parallel to the detection face of the housing, which sensor further includes a first permanent magnet disposed so that it magnetically biases the giant magnetoresistor in the direction of its sensitive axis xcex941 to a value such that the operating point is a point on a curve, representing the output signal of the giant magnetoresistor as a function of the value of the component of the magnetic field in the direction of the sensitive axis, which is situated in the vicinity of the middle of a substantially rectilinear portion of the curve.
If the component under test is made of a ferromagnetic material, the sensor advantageously further includes a second permanent magnet associated with an open magnetic circuit having two end surfaces of opposite polarity and situated against the detection face and on diametrally opposite sides of the electrical coil.
One embodiment of the invention will now be described with reference to the accompanying drawings.